The present invention relates to an optical disc in a sample servo format and an optical disc device.
In recent years, as media to record information optically, an optical disc, an optical card, an optical tape and so forth are proposed and developed. Among them, the optical disc is drawing attention as a medium that can record and reproduce information in a large capacity and of high density.
As for an optical disc capable of recording and reproduction, a magneto-optical (MO) disc is generally known. With regard to the optical disc system for performing recording and reproduction of various data by scanning concentric circular or spiral tracks formed on such an optical disc with a laser beam, corresponding to its rotation system, there are a ZCLV system, which performs recording and reproduction of data by dividing a recording area into zones including a predetermined number of tracks, reducing the number of revolutions in the optical disc stepwise moving from an inner circumferential zone to an peripheral zone, along with the movement of an optical pickup portion that shifts from the inner circumference to the periphery of the optical disc with an increased number of sectors per one circle (here, the number of revolution in each zone is constant), and allowing the linear velocity over the entire disc circle to be substantially constant, and a ZCAV system, which performs recording and reproduction of data by rotationally driving an optical disc with its recording area also divided into zones while maintaining a constant angular velocity.
Furthermore, an optical disc and an optical disc device in a continuous servo format, which performs a tracking control etc. by using pre-groups provided continuously along tracks, and an optical disc and an optical disc device in a sample servo format, which performs a tracking control etc. by using prepits in a servo area scattered on tracks, are known.
As an example of a conventional optical disc in the above-mentioned sample servo format, JP8(1996)-115523A describes an optical disc in which media information is recorded by the gray code in data areas of control tracks located in the vicinity of an inner circumferential end and in the vicinity of a peripheral end, and in a servo area of each segment, an identification mark providing information for distinguishing this segment by the recorded position within the servo area is formed together with two wobble pits used for tracking control etc. as three prepits. Then, an optical disc drive confirms whether the various pit patterns reproduced from the above-mentioned optical disc match the pit patterns in the predetermined servo areas, and thus, a rotational phase of the optical disc is synchronized with the phase of a servo clock. By using this servo clock, the position of the above-mentioned identification mark is read out to identify the segment, and at the same time, control information is obtained by reading out the media information recorded by the gray code.
Furthermore, as an example of a conventional disc not provided with the prepits as mentioned above but with pre-groups, JP10(1998)-320784A describes an optical disc in which a control track mark serving as a synchronization signal for a control track area and control information representing parameter information of a disc are recorded in the control track area by forming wobbles in a guide groove of each track, and a servo synchronization signal serving as a synchronization signal for a user area and address information of this sector are recorded in the user area etc., and a clock mark is formed in the guide groove.
However, the problem with the optical disc that specifies the servo area by confirming that the pit patterns reproduced by the optical disc drive match with each other for the three pits including the identification mark of different recording positions depending on the identification information of the segment and the two wobble pits, is that redundancy increases in a rewritable track area, which is a user area enabling writing.
Furthermore, a drive for this type of optical disc must obtain the control information by synchronizing the rotational phase of the optical disc with the phase of the servo clock by detecting whether the pit patterns match with each other in the servo area, identifying the segment by reading the position of the above-mentioned identification mark using this servo clock, and also reading the media information recorded by the gray code. Therefore, the circuit configuration for detecting whether the pit patterns are matched becomes complicated. At the same time, it takes time until the servo clock comes to a phase lock, and thus it is difficult to read out the control information in a short time.
Furthermore, in the case of the above-mentioned optical disc, in which not only the wobbles containing the synchronization signals and the control information or the address information independent of each other but also the clock mark are formed in the guide groove of the respective tracks, the optical disc is not only incompatible with the sample servo format but also difficult to be applied to high density recording by narrowing the track pitch.
Therefore, it is an object of the present invention to provide an optical disc in a sample servo format applicable to high density recording, in which a control track area is formed without reducing format efficiency of a rewritable track area, and also to provide an optical disc device that can read out control information in a short time with a simple circuit configuration.
To achieve the above object, an optical disc of the present invention is characterized in that a plurality of concentric circular or spiral tracks are formed in a control track area where control data are recorded, in the vicinity of at least one selected from an inner circumferential end and a peripheral end, and in a rewritable area located outside the control track area for recording user data at least in one direction selected from an inner circumference to a periphery and from the periphery to the inner circumference depending on the position of the control track area, and that a plurality of segments are formed in each track, each segment including a clock area where a clock mark is arranged, a servo area where a pair of wobble marks displaced in inner circumferential and peripheral directions from a center line of a track and separated by a predetermined distance in a circumferential direction, an address area where an address mark is arranged and a data area for recording the control data or the user data, wherein the clock mark, the wobble marks and the address mark are formed as prepits of an uneven shape, and, following the data area where the control data are recorded by the prepits of an uneven shape, a space of a predetermined length where the prepits do not exist is arranged for each segment in the control track area.
According to the optical disc of the present invention, in the rewritable track area, the data area following the address area, in which prepits of an uneven shape (hereinafter referred to as emboss prepits) do not exist and the user data are recorded magneto-optically, functions as a space, and a first emboss prepit in a segment immediately after this space easily can be specified as a clock mark. Furthermore, in the control track area, a first emboss prepit in a segment immediately after the space following the data area, where the emboss prepits exist and thus the control data are recorded, easily can be specified as a clock mark.
Therefore, the emboss prepits in the clock area, the servo area and the address area of each segment are not required to be arranged in unique patterns, and redundancy is not increased. As a result, the format efficiency in the rewritable track area can be enhanced.
In the optical disc of the present invention, it is preferable that the same control data are recorded in a plurality of tracks neighboring in the control track area.
According to this configuration, the emboss prepits of the control data are arranged identically in the radial direction, so that an optical disc device can read out the control data only by performing a focus control, without performing a tracking control of tracing the tracks precisely. As a result, the readout of the control data can be completed in a short time
Furthermore, in the optical disc of the present invention, it is preferable that the control data in the control track area are recorded by the run-length-limited code.
According to this configuration, even when the control data to be recorded continuously become either a logic 1 or a logic 0, by coding the data using the run-length-limited code, the emboss prepits actually recorded as the control data do not continue, and the optical disc device does not erroneously detect it as a space, so that the clock mark can be detected surely.
Moreover, in the optical disc of the present invention, it is preferable that the predetermined length of the space is a length exceeding a distance between the servo mark and a first prepit of the control data in the control track area.
According to this configuration, when the predetermined length is a length exceeding a distance between the servo mark and the first prepit of the control data in the control track area, the length of the control data in each segment can be set variably.
In order to achieve the above object, an optical disc device of the present invention is an optical disc device for driving an optical disc, in which a plurality of concentric circular or spiral tracks are formed in a control track area where control data are recorded, in the vicinity of at least one selected from an inner circumferential end and a peripheral end, and in a rewritable area located outside the control track area for recording user data at least in one direction selected from an inner circumference to a periphery and from the periphery to the inner circumference depending on the position of the control track area, and a plurality of segments are formed in each track, each segment including a clock area where a clock mark is arranged, a servo area where a pair of wobble marks displaced in inner circumferential and peripheral directions from a center line of the track and separated by a predetermined distance in a circumferential direction, an address area where an address mark is arranged and a data area for recording the control data or the user data, wherein the clock mark, the wobble marks and the address mark are formed as prepits of an uneven shape, and, following the data area where the control data are recorded by the prepits of an uneven shape, a space of a predetermined length where the prepits do not exist is arranged for each segment in the control track area, and the optical disc device is characterized in that the optical disc device includes reproduction means for reproducing pit signals corresponding to the prepits, clock mark detection means for detecting a pit signal following a distance of not less than a distance corresponding to the space length from the pit signals reproduced by the reproduction means as the clock mark, servo clock generating means for generating a servo clock synchronized with the clock mark detected by the clock mark detection means and control data readout means for reading out the control data based on the servo clock.
According to the optical disc device of the present invention, with the use of the clock mark detection means, in the rewritable track area, a reproduced pit signal, which follows a distance after the address area corresponding to the length of the data area where the emboss prepits do not exist and the user data are recorded magneto-optically, can be detected as a clock mark, whereas in the control track area, a reproduced pit signal, which follows a distance corresponding to the length of the space following the data area where the emboss prepits exist and thus the control data are recorded, can be detected as a clock mark. As a result, a servo clock having a phase synchronized with a clock mark, that is, with the rotation of the optical disc, can be generated easily.
Therefore, for generation of a servo clock, it is no longer necessary as conventionally to arrange the emboss prepits in the clock area, the servo area and the address area of each segment in unique patterns and to achieve a phase synchronization of a servo clock by matching the patterns of the reproduced pit signals with the unique patterns, so that a pull-in speed of a phase lock can be improved with a simple circuit configuration.
It is preferable that the optical disc device of the present invention further includes tracking control means for controlling a center of an optical beam spot to be emitted on the optical disc to match a center line of a track, based on the results of the pair of wobble pits reproduced by the reproduction means and servo control means for setting the tracking control means in a non-operating state at the time when the control data is read out by the control data readout means, wherein the same control data are recorded in a plurality of tracks neighboring in the control track area of the optical disc.
According to this configuration, the emboss prepits of the control data are arranged identically in the radial direction, so that the optical disc device can read out the control data only by performing a focus control, without performing a tracking control of tracing the tracks precisely. As a result, the readout of the control data can be completed in a short time.
Furthermore, in the optical disc of the present invention, it is preferable that the control data in the control track area are recorded by the run-length-limited code, and that the control data readout means includes decoding means for decoding the control data recorded by the run-length-limited code.
According to this configuration, even when the control data to be recorded continuously become either a logic 1 or a logic 0, by coding the control data using the run-length-limited code, the emboss prepits actually recorded as the control data do not continue, and when they are reproduced as pit signals, the clock mark detection means does not erroneously detect it as a distance of not less than a space length, so that the clock mark can be detected surely.